Pollutant Information: Sulphur Dioxide

About Sulphur Dioxide

Category: Air pollutants

Sulphur dioxide (SO2 expressed as SOx) has long been recognised as a pollutant because of its role, along with particulate matter, in forming winter-time smog. Studies indicate that SO2 causes nerve stimulation in the lining of the nose and throat. This can cause irritation, coughing and a feeling of chest tightness, which may cause the airways to narrow. People suffering from asthma are considered to be particularly sensitive to SO2 concentrations. Fuel combustion accounted for 94% of UK SO2 emissions in 2015 with the main source being the combustion of solid fuel, mainly coal, which has a high sulphur content, relative to other fuels. SO2 emissions can be calculated from knowledge of the sulphur content of the fuel and from information on the amount of sulphur retained in the ash.

Since 1970, SO2 emissions have declined by 96%. The time series exhibits a steady decline between 1970 and 2009 with the exception of small peaks in 1973 and 1979 corresponding to the harsh winters in those years and a short period at the end of the 1980s when emissions were relatively constant from year to year. The long-term reduction has been due to switching to alternative fuels from solid fuels, improved abatement technology and more stringent legislation on the sulphur content of some fuels. Since 2009 sulphur emissions have flattened out, and in some years increased slightly, mostly due to a short-term increase in coal use by the power sector. Emissions from the power sector decreased by 26% between 2014 and 2015, largely due to a decrease in coal use.

The largest source of SO2 emissions is public electricity and heat production, which accounted for 38% of total emissions in 2015. Since 1970 there has been a gradual decline in coal use in power stations, and flue-gas desulphurisation has been increasingly used to abate the SO2 emissions, so the emissions from power stations in 2015 were only 3% of the level in 1970. Coal consumption by, and therefore SO2 emissions from, other sectors have also declined so coal-fired power stations remain the most significant source of SO2 emissions despite the big reductions achieved by the sector. Road transport emissions account for less than 1% of the total SO2 emissions. Since the early 1990s, road transport emissions have declined with the reduction in the sulphur content of Diesel Engine Road Vehicle (DERV) and petrol. Similarly the reduction in sulphur content of gas oil is reflected in the emissions from off-road vehicles and domestic and commercial heating where gas oil is used extensively. Emissions of SO2 from industry result mainly from the combustion of coal and fuel oil, some refinery processes and the production of sulphuric acid and other chemicals. Between 1970 and 2015 emissions from industrial combustion sources have fallen by 97% though most of the decrease took place between 1970-1985 reflecting the decline in the energy intensive iron and steel industry and other heavy industries. There has also been a decline in the use of coal and fuel oil in favour of natural gas. Emissions in 2015 are 19% below the UK's National Emission Ceilings Directive and Gothenburg Protocol targets for 2020.

Time series graph

Notable events

Power Station Flue Gas Desulphurisation (FGD) abatement equipment installed. By 2008 FGD contributed between 1/4 and 1/3 of total emissions reductions from power stations.

Decrease in emissions

1984

1985

Combustion in Industry/Residential/Commercial

1984 miners' strike led to a significant decrease in the use of coal for combustion in electricity generation. A noticeable dip in emissions from coal-fired combustion sources in 1984 but increase in use of alternative fuels (e.g. Oil) and resulting emissions of pollutants (Cadmium & Lead).

Decrease in emissions

1981

2011

Combustion in Industry/Residential/Commercial

Restriction on use of smoke producing fuels in urban areas, switch from coal and oil to natural gas and from 2006 reduction in sulphur content of gas oil

Decrease in emissions

2009

2012

Public Electricity and Heat Production

The economic downturn has caused significant reductions in energy demands and many industries have made cut backs or closures, resulting in reduced emissions.

Decrease in emissions

2010

2012

Public Electricity and Heat Production

As a result of the economic downturn the drive to cut energy costs has resulted in an increase in solid fuel use, particularly in 2012 some coal-sensitive pollutants have seen a significant rise in coal burning emissions.